• IP protocol has no error reporting or error correcting mechanism and
• It does not support host and management queries. A host sometime need to determine if a router or a host is alive.

Thus ICMP works as a companion to the IP protocol to compensate for the above two deficiencies.

ICMP messages are divided into two broad categories:

• Error Reporting Message
• Query Message

Note:

• There is no ICMP error message generated for any ICMP message itself.
• It is not generated for multicast address and fragmented datagram and special address such as loopback (127.0.0.1 or 0.0.0.0).
• ICMP always reports error messages to the original source

Categories: Networking